INLET CROSS-SECTIONAL AREA CALCULATED BY PROCESS-BASED MODEL

Abstract

This paper introduces a process-based model for calculating the equilibrium cross-sectional area of a tidal inlet and temporal behavior of small perturbations in channel area from equilibrium. The model accounts for the dynamic balance between inlet ebb-tidal transport and longshore sand transport at the inlet entrance. Expressed in terms of a water discharge through the inlet and the gross longshore sand transport rate, the formulation can account for tidal, river, and wind-driven flows. The resultant predictive equation recovers the form of the well-known empirical formula AE = CPn, where AE is the equilibrium (minimum) cross-sectional area, P is the tidal prism, and C and n are empirical coefficients. An explicit expression is obtained for C in terms of coastal sediment-transport processes, and the value of n derived is in the range found empirically. The process-based model qualitatively predicts the difference in trends in inlet crosssectional area on wave-sheltered and fully-exposed coasts. In time-dependent mode, the model reproduces qualitative behavior of the departure of the crosssectional area from equilibrium under perturbations in the driving forces of discharge and waves.